1. Field of the Invention
The present invention relates to a solenoid valve for a brake system, and more particularly, to a solenoid valve for a brake system capable of being more easily manufactured and reducing manufacturing costs.
2. Description of the Related Art
Generally, an anti-lock brake system for vehicles serves to prevent locking of wheels by sensing slippage of the wheels and suitably controlling braking pressure applied to the wheels. The anti-lock brake system prevents the wheels of the vehicle from skidding during braking, whereby the steering performance of the vehicle is maintained, and the vehicle is stopped safely.
In order to control braking pressure, the brake system includes a plurality of solenoid valves to open or close an oil path of a braking hydraulic pressure line. The solenoid valves include normal open type solenoid valves which are normally kept in an opened state, and normal close type solenoid valves which are normally kept in a closed state.
FIG. 1 shows a conventional normal close type solenoid valve. A conventional normal close type solenoid valve includes a valve housing 3 press-fitted in a bore 2 of a modulator block 1, a cylindrical sleeve 4 coupled to the valve housing 3, a valve core 5 coupled to the sleeve 4 at an opposite side of the valve housing 3, and an armature 6 slidably mounted in the sleeve 4. The solenoid valve further includes a valve seat 7 press-fitted in the valve housing 3, the valve seat 7 having a first orifice 7a, and an opening/closing member 8 slidably mounted in the valve housing 3, the opening/closing member 8 being formed at an upper portion thereof with a second orifice 8a that is smaller than the first orifice 7a and also, being formed at a lower portion thereof with an opening/closing portion 8b to open or close the first orifice 7a. 
When the armature 6 is moved toward the valve core 5 by a magnetic force, the smaller second orifice 8a is opened first. Then, the larger first orifice 7a can be opened as an opening spring 9 pushes the opening/closing member 8 up under a reduced pressure difference between upstream and downstream of the second orifice 8a. This results in easy opening of an oil path even with a low force.
As described above, the conventional solenoid valve is constituted such that the valve housing and the valve seat are separately provided, and the valve seat is press-fitted in the valve housing. However, the conventional solenoid valve as constituted above has problems of a great number of components, complicated structure, and difficult manufacture. Accordingly, manufacturing costs of the valve are high.
Further, because the sleeve and the valve core are coupled to each other through a welding process, and also the sleeve and the valve housing are coupled to each other through a welding process, the above-described conventional solenoid valve has shortcomings of high work effort and low assembly productivity.